A piston ring used in an internal combustion engine is installed inside a ring groove which is formed in a side face of a piston. An outer peripheral face of the piston ring is in sliding contact with an inner wall of a cylinder bore. For example, Patent Literatures 1 to 5 describe a piston ring in which a part or all of an outer peripheral face is covered with a hard coating. Patent Literature 6 describes a piston ring provided with a titanium nitride film, which is formed by an ion plating method, as a hard coating.